Steam and combustion products generator with expansion means to dry the steam



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w. L. SANBORN 2,568,662 STEAM AND COMBUSTION PRODUCTS GENERATOR WITH EXPANSION MEANS TO DRY THE STEAM Filed Sept. 21. 1946 2 Sheets-Sheet 1 2 2 r w m M n W mm a I). r I. 7 W 1 W P 1951 w. L. SANBORN STEAM AND COMBUSTION PRODUCTS GENERATOR WITH EXPANSION MEANS TO DRY THE STEAM Flled Sept 21 1946 2- Sheets-Sheet 2 Patented Sept. 18, 1951 mrso A TENT OFFICE .DBY THE STEAM Winni L sensual, Milwaukee, Wis.

- Application September 21, 1946, Serial No. 698,459

2 Claims. V 1

My invention relates to methods and devices for generating heated gaseous fluids for such purposes as supplying heat and power.

An object and a ieature of my invention is the combining of a combustion gas generator and a vapor generator with certain important advantages. The combination may be regarded as primarily a combustion gas generator supplemented by a vapor generator, or may be re garded as primarily a vaporgenerator with auxiliary use of the concurrently produced gases of combustion. Theobjects and advantages of the invention may be appreciated by considering the invention in these two aspects in turn,

'An important object of theinvention as a combustion as generator is to employ combustion gases for heat .or' power purposes at only moderate temperatures asdistinguished'from the exceedingly .highldestructive temperatures characteristic of many combustion gas generators, and to vdo so withoutsacriflcing the energy inherent in the high temperature gases. In this regarda .feature of the invention is the concept of adding water vapor to high temperature come bustion gases thereby to obtain a gaseous a gaseous mixture at what may be termed moderate temperature without material loss in energy, It is an important fact that whereas the neat contained in combustion gases is substantially entirely sensibleheat, alarge portion of the heat in my resultant mixture is. latent heat of vaporization. I

, As a combustion gas generator a further object of my invention is to avoid damaging the metal walls of a gaseous fluid generator system by, exceedingly high temperatures. The addition of water vapor to the high temperature combustion gases avoids such damage after the addition is made. Prior to the addition I confine the high temperature gases solely by metal walls that are cooled by a fluid medium. By employing fluid; cooled walls for confinin the generated gaseous medium up to the point of vapor introduction and by introducing suf flcient vapor to bring the resultant mixture down to 'a moderate temperature range, the life of the flre tube is greatly prolonged.

Another important object of the invention as a combustion gas generator is to minimize the usual heat losses --by radiation. Any flrebox that is separated from the atmosphere solely by metal Walls will lose a great amount of heat to the atmosphere by radiation. I propose to reduce this loss by. employing acombustion chamher having .a surrounding. jacket containing a fluid medium so that the heat conducted through the metal wall of the firebox is transmitted to the fluid medium instead of to the atmosphere, the jacketed structure functioning as a heat exchanger. In employing the continually heated fluid medium for a useful purpose I salvage or reclaim a substantial proportion of heat that otherwise would be lost.

In some practices of my invention the heated fluid medium is used as a power source, for example, by driving a suitable turbine. The turbine or other power device may perform use- .ful functions in the operation of the combustion generator, such as the function of conveying fuel to combustion zone, or the function of supplying the combustion zone with air under forced draft. A featureof the preferred practics of my invention is the generation of steam under pressure in the firebox jacket and the use of the steam in an ejector to facilitate the flow .of air to the combustion Zone by Venturi action, as well as to prevent the gaseous fluids under pressure on the discharge side of the generator from flowing back through the combustion zone.

When the invention is viewed as primarily a boiler or vapor generator, an outstanding advantage is the salvaging of certain fuel losses that occur in conventional boiler operation, the salvaging being accomplished by mixing the combustion gases with the generated vapor to obtain a resultant high-energy mixture of gaseous fluids. Thus the invention avoids well known losses that go up the flue in conventional steam boiler operation, including the lossesv represented by the sensible heat in the chimney gases and losses involved in the production of steam in the combustion chamber, the water for the steam being derived from the fuel and the air supply as well as producedby the combustion of hydrogen in the fuel.

More specific objects sought in the combined gas and vapor generator are to insure the p duction of a dry vapor for mixture with the combustion gases by certain expedients, such as flashing or superheating, and to provide for suitable turbulence for quickly in-termixing the vapor and combustion gases to such extent as to produce a substantially homogeneous gaseous fluid.

Other objects and advantages will be apparent in the following more detailed description taken with the accompanying drawings.

In the drawings, which are to be regarded as merely illustrative:

Fig. 1 is a perspective View of a preferred embodiment of the invention;

Fig. 2 is a longitudinal sectional view on line 22 of Fig. 1, of the preferred embodiment;

Fig. 3 is a transverse section taken as indicated by the line 33 of Fig. l and Fig. 4 is a fragmentary view similar to Fig. 2, showing a modified form of the invention.

The principal parts of the first embodiment of the invention shown in Figs. 1 and 2 include a hollow boiler generally designated la, a fire tube generally designated l l' surrounded by the boiler, a burner generally designated l2, at one end of the fire tube H, and a mixing chamber l3, at the other end of the fire tube.

The boiler I has an outer shell [5, an inner end wall It and a front end wall H, the fire tube H serving as an inner cylindrical wall for the boiler. To permit longitudinal thermal expansion of the fire tube H independent of expansion and contraction of the boiler shell l5, the boiler shell is enlarged or conically flared at one end as indicated at 18 to give the front Wall H a relatively large diameter. In such a construction the extensive front wall I! afiords suflicient flexibility to accommodate differences in longitudinal expansion between the shell and the fire tube without breakage.

The boiler may be supplied by suitable means including a boiler feed pipe 20 and the normal water level may be so that approximately twothirds of the fire tube II is water covered.

Any suitable burner may be employed to fire the boiler, as for example the one shown in my application entitled Method and Apparatus for Burning Comminuted Fuel, filed September 2 1946, Serial No. 698,458, now abandoned, and which isc' aracterized by the ability to produce a flame on the order of 3000" F. or higher. The

burner is indicated at l2, and has appropriate controls for full modulation of the fire, as disclosed in said application. Any other burner, having equivalent operating characteristics, would be satisfactory. The cylindrical casing 2| of the burner I2 is shown abutting the front boiler wall I! with the nozzle 22 of. the burner directed towards the fire tube ll coaxially thereof. If, desired, the movable flame control shield M of the burner may be appropriately dimensioned to telescopewithin the enlarged end of the fire tube II, which tube serves as a combustion chamber for the dual purpose of generating gases of combustion and of heating the liquid to produce vapor under pressure in the boiler l0.

The mixing chamber it may be formed as shown by extending the boiler shell and adding an end wall 23. The fire tube ll terminates in the mixing chamber l3 thereby forming an inlet for the mixing chamber and the mixing chamber is provided with at least one outlet 25, through which outlet the ultimate gaseous fluid may be conducted to a point of use, or discharged as a jet for jet propulsion.

It is contemplated that the wet vapor generated in the boiler ID will be discharged into the mixing chamber l3 in a super-heated state or at least in dry vapor form and that suitable expedients will be provided for drying the vapor' One possibility is to dry the generated wet vapor by expansion thereby to cause liquid particles to flash into vapor. Another possibility is to apply suificient heat to the generated vapor to insure vaporization of all liquid particles therein. In the a present embodiment of the invention I provide for drying the vapor both by expansion and by added .bustion gases generated by the burner 12.

4 heat. In some practices of the invention either one of the two expedients may be relied upon alone to attain the result.

I have found that the best results are obtained when the steam taken from the boiler H] for mixing with the combustion gases is reduced in pressure in several stages, with heat being applied at least in the last stage to insure that perfectly dry steam vapor will be discharged into the mixing chamber i3 with the combustion gases.

As best shown in Fig. 2 a vapor duct generally designated 26, that conveys the vapor from the boiler to the mixing chamber I3 is progressively increased in diameter by stages for expansion of its vapor content and extends into the fire tube II to cause heating of the vapor content by the heat of combustion. The vapor duct 26 includes a relatively small diameter pipe 2? on its receiving end at the boiler l0, this pipe being provided with an adjustable valve 28. The valve 28, shown as a simple manual valve, acts as an adjustable restriction and provides the first stage of expansion of the vapor stream for flashing liquid particles into vapor. The second stage of expansion occurs when the vapor passes from the small pipe 21 to a continuing pipe 30 of somewhat larger diameter. Preferably the pipe 30 extends into the mixing chamber l3 as shown to derive heat from the hot gaseous content of the mixing chamber. The third stage of expansion in the vapor duct 26 occurs when the vapor passes from the pipe 30 into a still larger continuing pipe 3|. At this point the vapor passes into the still hotter zone in the interior of the fire tube II.

It is to be noted that a substantial longitudinal portion of the pipe 3| lies inside the fire tube H to provide extensive areas for heat transfer from the gases of combustion in the fire tube to the vaporcontent of the pipe, and to provide ample time for heat transfer to the vapor stream, the pipe being doubled back on itself for this purpose I have foundv that such an arrangement insures the conversion of the wet vapor from the boiler into perfectly dry vapor at the point of discharge into the mixing chamber l3.

Preferably the mixing chamber 13 is so de signed as to create sufficient turbulence to intermix the vapor and the gases of combustion of the composite inflowing stream into a resultant homogeneous gaseous stream. To promote such turbulence, the mixing chamber may have at least one baffle 29. Other baffles may be used either with baflle 29 or in place of it, to obtain the desired mixing of the dry steam vapor with the products of combustion from the burner l2.

The manner in which the described apparatus operates may be readily apparent from the foregoing description The burner l2, which has a suitable blower (not shown), projects fuel in finely divided form into the fire tube II along with a forcefulenveloping stream of secondary air to cause combustion at a high temperature, say on the order of 3000 F. or higher.

The vapor produced'under pressure by the boiler I0 is discharged from the vapor duct 26 with relatively high velocity and the position of the discharge end of the vapor duct shown in Fig. 2 causes the kinetic energy of the vapor stream to be transmitted to the streamof com- An efiect of the vapor discharge into the mixing chamber IS in the manner shown and described is the acceleration of flow of the combustion gases from the fire tube into the mixing chamber which effects a pressure reduction inthe fire tube thereby enabling 'full combustion of fuel to take placetherein, and promoting the how of secondary air fromthe atmosphere through the burner into the fire tube, to support combustion. A second effect of the ejector action is the prevention of back fiow from the mixing chamber l3 into the fire tube H. In fact the pressure in the mixing chamber 13 may be somewhat higher than the pressure in the fire tube II by virtue of the discharge from the vapor duct 26. i

It is important to note that all of the metal surfaces confining the gases of combustion in the fire' tube H- up to the point where the combustion gases enter the mixing chamber 13 are cooled metal surfaces, the cooling medium being the liquid and vapor inside the boiler I0. Thus the boiler 16 serves in effect as a cooling jacket to keep the high temperature combustion gases from deteriorating the metal of the fire tube. In the mixing chamber l3 beyond the fire tube lithe metal walls confining the gaseous fiuid generated by the apparatus are not fluid-cooled but the intermixture of the vapor with the gases of combustion results in temperatures low enough to avoid damage to uncooled metal surfaces.

It will also be noted thatin the form of the invention, the steam tube 26 does not have to pass through the fire tube H, where differences in the expansion between the .fire tube II and boiler shell 15 would create difliculties.

'More specific information about an embodiment of the invention'that. has been successfully operated with surprisingly high efiiciencies may behelpful. 1 In this illustrative embodiment of the invention, the fire tube H is :6 inches inside diameter at its inlet end and is stepped down to 3 /2 inches inside diameter. The fire tube is preferably made of a-nickel base alloy having 11 to 22% chromium, commonly referred to as Nichrome alloys. The pipe 27 is /2 inch standard u pipe, the pipe 30 is inch standard pipe, and the pipe 3| is 1 inch standard pipe, the latter two pipes being constructed of 12 gauge stainless steel (18-8). The highest temperature in the fire tube is probably on the order of 3300-F., but drops in the region of the fire tube occupied by the vapor duct 26 and has been measured by observation in that region at approximately 3,020 F. The boiler pressure is approximately 12 pounds per square inch and the temperature of the steam as it reaches the valve 28 is approximately 240 F., but the steam discharge from the vapor duct 26 into the mixing chamber has a temperature on the order of 480 F. The pressure in the mixing chamber I3 is on the order of 3 pounds and the homogeneous gaseous mixture discharged through the outlet 25 from the mixing chamber is approximately 1200 F. With the burner using 21 pounds of heavy fuel oil per hour at 19,600 13. t. u.s per pound, and with the boiler taking 192 pounds of water per hour at 56 F., 16,800 cu. ft. of gaseous fluid will be discharged per hour through the outlet 25 which has a 1 inch inside diameter and is 2 inches long, at the stated pressure of 3 pounds per square inch. The burner under the conditions stated uses approximately 5400 cubic feet of air per hour, at relative humidity and F. temperature and in operation the CO2 content in the mixing chamber I3 is 11.5% S. T. P. before the steam is introduced through the valve 28,

rected towards the mixing chamber 6 and is reduced to only 19.5% S. T. P. when the steam is introduced. The total electrical energy input into the'burner including the blower for the'burner air supply is on the order of 3 horse power.

The purpose of Fig. e is to indicate how the invention may take a second form in which auxiliary power is derived from the vapor duct 26 and in which the Vapor is discharged from the vapor duct 26 with highly effective ejector action.

The form of the invention shown in Fig. 4 is in large part identical in construction with the first described embodiment asindicated by the use of correspondingnumerals 'toidentify corresponding parts. The construction of the boiler l6 and the-mixing chamber 23 are unchanged except that the discharge end of the fire tube H constituting the inlet to the mixing chamber i3 is constricted to form 'what may be termed'a enturi throat 32.

I propose to form two concentric streams at the throat 32 with one of the two streams serving as an ejector to promote the flow of the other stream. I prefer to'znake the vapor stream the center stream, although the advantages of'the reverse arrangement may be controlling in some practices of the invention.

The vapor duct 36 in Fig. 4 corresponding to the vap-orduct 26 in the first embodiment of the invention includes a relatively small pipe 3-! that receives the vapor from the boiler l6 and discharges the vapor into a suitable turbine 33, which may be used to drive the burner mechanism after it has been initially started by other means. -On the low pressure-side of the turbine 33 the vapor duct 36 is continued by a somewhat larger pipe 38 of inch diameter, againby a larger pipe 39 of 'one'inch diameter and finally is continued by a still larger pipe 46 of 1% inch diameter. Thus the first stage of the expansion of the vapor stream in the vapor duct 36 is in the passing of the vapor stream through the turbine 33 (although this does not aid materially, if at all, in the drying of the steamdue to-the work done in'driving the turbine), the second stage is in passing into the pipe 39 and the third stage is the passing into the pipe 40.

The pipe 46 enters the fire tube ll laterally thereof, but before doing so forms a liberal loop 4| to afiord sufficient flexibility to follow longitudinal thermal expansion and contraction of the fire tube relative to the boiler shell. The pipe 36 extends inside the fire tube along the axis thereof and terminates in a nozzle 42 di- I3. The nozzle 42 preferably terminates somewhat short of the Venturi throat 62. It is apparent that the relation of the nozzle 42 to the throat 32 is such as to produce a highly effective ejector effect for promoting fluid flow into the mixing chamber I3 and for preventing back flow from the mixing chamber into the fire tube H.

It will be apparent to those skilled in the art that either the stream of vapor discharged from the vapor duct 36 or the stream of combustion gases generated by the burner may dominate in the ejector effect, the dominating stream transmitting kinetic energy to the other stream. Thus in one practice of the invention the vapor discharge may actively contribute to the velocity of the gases of combustion while in another practice of the invention the relatively high velocity of the gases of combustion may desirably facilitate the flow of vapor through the vapor duct 36.

I have also found that the temperature of the V asoaeoe discharge gases at the outlet 25 may be very simply controlled by varying the amount of steam introduced through the pipe 26; the more steam that is introduced, the lower the temperature of the gaseous mixture discharged through the outlet 25, and conversely, the less steam that is introduced, the higher the temperature of such gaseous mixture. However, there should be a minimum steam content sufli'cient to protect the metals in contact with the hot gases, as hereinbefore described.

In this connection it is important to note that unless the steam that is introduced into the mixing chamber I3 is absolutely dry, it will kill the fire and make it'impossible to obtain the operating characteristics that have been heretobefore described.

1 The dryness of the steam is also important to protect the metal surfaces for I have found metal will deteriorate rapidly if any water particles are in the superheated steam, and to obtain dry superheated steam it is highly desirable to cause the steam to experience successive pressure drops while continually applying heat.

It is understood, of course, that the boiler will be equipped with the usual controls including a pressure regulated escape valve 43, so that when the boiler is generating more steam than is required for the gaseous mixture the excess steam ma be used elsewhere.

It will be noted that in both embodiments of the invention there are several successive pressure drops for the steam before it is introduced into the mixing chamber l3, and that the second and succeeding pressure drops take place under the influence of heat.

My description in specific detail of the selectiveaembodiments of the invention will suggest to those skilled in the art various changes and substitutions in my concept, and I reserve the right to all such departures from my description that lie within the scope of the appended claims.

I claim:

1. A method of generating hot gaseous fluid. including the steps of burning fuel to obtain a stream of combustion gases, applyingthe heat of combustion to a liquid to obtain a stream of wet vapor under pressure, reducing the pressure of said wet vapor stream in a plurality of stages to dry the stream by flash action, and intermingling the two streams.

2. In an apparatus for generating heated gaseous fluid, means forburning fuel in a combus tion zone, a boiler adjacent said combustion zone to receive heat therefromfor generating vapor, means to expand the vapor in successive stages to flash all water particles therein, and means to mingle the dried vapor with the gases of combustion from said zone to produce a heated as and vapor mixture.

1 WILLIAM- L. SANBORN.

REFERENCES CITED The following references are of "record in the file 'of this patent:

v UNITED STATES PATENTS Number Name Date 601,456 Woillard Mar. 29,1898 868,372 Tate Oct. 15, 1907 947,107 Lamson Jan. 18, 1910 1,019,278 Restucci Mar. 5, 1912 1,058,850. Deemar Apr.15, 1913 1,063,953 Caille June 10, 1913 1,142,271 Rinehart June 8, 1915 1,168,298 Gibson Jan. 18, 1916 1,243,812 Clutter Oct. 23, 1917 1,988,456 Lysholm Jan. 22, 1935 2,019,694 Reitlinger Nov. 5, 1935 2,359,108 Hoskins Sept. 26, 1944 FOREIGN PATENTS Number Country Date 168,508 Germany Mar. 20, 1906 655,532 Germany Jan. 18, 1938 OTHER REFERENCES Heat Power Engineering by Barnard et al., 1926, Part I (Figure 15 facing page 34). 

